In recent years, attention is received by vehicles which have a assembled battery that serves as the power source of the vehicles. The assembled battery of this type includes a monitoring section which monitors the charge and discharge state (for example, overcharge and overdischarge) of the assembled battery on the basis of information acquired by a voltage detection circuit included in the monitoring section. On the other hand, such a case in which an abnormal event may occur in the voltage detection circuit itself can also be conceived. Thus, in order to detect the overcharge and overdischarge with accuracy, it is necessary to adequately execute a self-diagnosis of the voltage detection circuit. That is, there is a possibility that the overcharge and overdischarge of the assembled battery can be overlooked unless the chance of the self-diagnosis is adequately ensured.
Disclosed in Patent Literature 1 is an overcharge detector for an on-board secondary battery to which charge and discharge control is provided in accordance with a charge control target value during the operation of the vehicle. The overcharge detector for the on-board secondary battery includes: a first overvoltage detection circuit for detecting an overcharge of the secondary voltage; a second overvoltage detection circuit for detecting an overcharge of the secondary voltage, the second overvoltage detection circuit being provided in parallel to the first overvoltage detection circuit; and a self-diagnosis section configured to execute a self-diagnosis for detecting an abnormal event in the first and second overvoltage detection circuits when the operation of the vehicle is ended. In the overcharge detector with the above-configuration, the self-diagnosis section includes: a diagnosis start determination section for directing the execution of the self-diagnosis on conditions that at the time of the request for the self-diagnosis, the voltage of the secondary battery is within a predetermined voltage range that permits the self-diagnosis of the first and second overvoltage detection circuits; and a change request section for requesting a change in the charge control target value during the next operation of the vehicle to a value higher than the current value when the diagnosis start determination section has determined that the voltage of the secondary battery at the time of the request for the self-diagnosis is lower than the predetermined voltage range.